Abstract: The present invention provides a reduced wire count voltage-drop sense system and method wherein the voltage drop across a load device is determinable using only one sense lead regardless of the number of load devices. In one embodiment, the voltage drop across any one of four LEDs (220A-D) in a photoplethysmographic probe when a drive current is applied therethrough via one of four input drive leads (230A-D) connected to separate LED terminals (222A-D) is determinable from a first voltage drop and a second voltage drop, for example, by subtracting the second voltage drop, or a portion thereof, from the first voltage drop. The first voltage drop is measurable across a terminal (232A-D) of the input drive lead (230A-D) connected to the LED (220A-D) across which the voltage drop is to be determined and a terminal (252) of a sense lead (250) connected to a common LED terminal (224).

Abstract: A system and method of reducing cross talk in pulse oximetry signals that are attenuated by a patient tissue site are provided. In one embodiment, Red and IR LEDs of a pulse oximeter are separately excited (1010) and the respective Red and IR data vectors output by the detector are measured (1020). The Red and IR data vectors are normalized (1030) to unit length Red and IR data vectors. Red to IR and IR to Red cross talk vectors are computed (1040). The Red to IR cross talk vector may be computed as a vector having a length equal to the dot product of the normalized Red and IR data vectors with its direction being opposite that of the normalized IR data vector. The IR to Red cross talk vector may be computed as a vector having a length equal to the dot product of the normalized Red and IR data vectors with its direction being opposite that of the normalized Red data vector.

Abstract: A pulse oximeter (100) includes two or more light sources (102) for transmitting optical signals through an appendage (103) of patient. The sources (102) are operated to transmit code division multiplexed (CDM) signals. That is, the sources (102) are driven by drives (104) in response to signals from a digital processing unit (116) such that the sources (102) are modulated using different code sequences. The code sequences are preferably non-periodic and may be orthogonal to one another. The use of such CDM signals provides certain advantages related to noise reduction.

Abstract: An oversampling pulse oximeter includes an analog to digital converter with a sampling rate sufficient to take multiple samples per source cycle. In one embodiment, a pulse oximeter (100) includes two mor more light sources (102) driven by light source drives (104) in response to drive signals from a digital signal processing unit (116). The source drives (104) may drive the sources (102) to produce a frequency division multiplex signal. The optical signals transmitted by the light sources (102) are transmitted through a patient's appendage (103) and impinge on a detector (106). The detector (106) provides an analog current signal representative of the received optical signals. An amplifier circuit (110) converts the analog current signal to an analog voltage signal in addition to performing a number of other functions. The amplifier circuit (110) outputs an analog voltage signal which is representative of the optical signals from the sources (102).

Abstract: An inventive apparatus and method as disclosed for the automatic identification of a given one of a predetermined plurality of cuff assemblies interconnectable to a sphygmomanometer for use in a blood pressure measurement procedure. The invention provides for the obtainment of a pressure measurement(s) during deflation of an inflatable cuff, and utilization of such measurement(s) to identify the cuff assembly. More particularly, each different cuff assembly may be provided with a corresponding gas-flow restrictor which allows the pressure measurement(s) made during deflation of a given cuff assembly to be correlated in fashion that allows for identification. Preferably, first and second pressure transducers are provided for automatic pressure measurements both upstream and downstream of a cuff assembly during the deflation portion of a cuff identification operation.

Abstract: A system is provided for improving photoplethysmographic analyte measurements by de-emphasizing motion-contaminated data and/or emphasizing motion-free data. The system 100 is used in a measurement instrument which includes at least illumination source 104 for transmitting at least two light signals at two center wavelengths through a patient's appendage 106 and a sensor 108 for converting the light signals transmitted through the appendage into electrical output signals. The system 100 includes a first buffer 116 configured to temporarily store at least one pulse cycle of output signals received from the sensor 108. A motion estimator 122 quantifies an amount of motion associated with the output signals stored in the first buffer 116 by performing a principal component analysis on differential absorption values derived from the output signals. Based on the amount of motion estimated, a weight application module 118 is configured to associate a weight with the output signals in the first buffer.

Abstract: An oversampling pulse oximeter includes an analog to digital converter with a sampling rate sufficient to take multiple samples per source cycle. In one embodiment, a pulse oximeter (100) includes two mor more light sources (102) driven by light source drives (104) in response to drive signals from a digital signal processing unit (116). The source drives (104) may drive the sources (102) to produce a frequency division multiplex signal. The optical signals transmitted by the light sources (102) are transmitted through a patient's appendage (103) and impinge on a detector (106). The detector (106) provides an analog current signal representative of the received optical signals. An amplifier circuit (110) converts the analog current signal to an analog voltage signal in addition to performing a number of other functions. The amplifier circuit (110) outputs an analog voltage signal which is representative of the optical signals from the sources (102).

Abstract: An improved method and apparatus is disclosed for use in frequency division multiplexed spectrophotometric systems. In photoplethysmographic applications the invention provides for the modulation of a plurality of light sources at different frequencies and in accordance with a predetermined phase relationship. Light from the sources that is transmitted through a tissue under test is detected at a detector. A composite signal indicative of the intensity of light received at the detector is demodulated based on the different modulation frequencies and predetermined phase relationship to obtain signal portions corresponding with each of the light sources. Modulation and demodulation are synchronized during each measurement period. The modulation waveforms used to modulate the light sources and corresponding demodulation waveforms used to demultiplex the composite signal are symmetrically timed about a center point for each of the measurement periods.

Abstract: A novel process is disclosed for continually or periodically correcting gas spectrometer measurements for wavelength calibration drift without interrupting the gas measurement process. The spectrometer employs certain calibration vectors for use in obtaining single component information based on a composite measurement for a multi-component gas sample. A calibration vector can be provided for each component of interest as well as an average spectrum and other spectra as desired. These calibration vectors are used to selectively compensate for spectral interference between the multiple components so as to effectively isolate and measure a selected spectral characteristic for a particular component of interest. Temperature changes and attendant variations in spectrometer dimensions or other temperature related factors can degrade measurement performance.

Abstract: The respiratory gas analyzer (10), in one embodiment, is used for in-stream analysis of a patient breathing circuit (12). The analyzer includes a source (12) of infrared illumination, a modulator (28) for modulating the infrared illumination on a wavelength dependent basis to yield a modulated signal, a transmitter/detector unit (32) for transmitting the modulated signal through the breathing circuit (12) and detecting the transmitted signal, and a processing unit (34) for determining composition information regarding a sample under analysis based on the detected, modulated signal. The modulator (28) may include, for example, a Michelson interferometer for transforming the illumination into a frequency domain signal. The modulated signal allows for use of a compact detector system at the respiratory circuit interface. In addition, infrared fiber optics can be utilized to minimize instrumentation/optics at the interface.

Abstract: A desired mass domain excitation profile is selected and converted to a frequency domain excitation spectrum in which the frequency of excitation is generally proportional to the inverse of the mass-to-charge ratio. In the direct method of the invention, the specified frequency domain spectrum is converted by inverse Fourier transformation to a time domain waveform and multiplied by an expanded window function. The time domain waveform is forward Fourier transformed to produce a second discrete frequency spectrum each frequency of which is assigned a phase scrambled such that maximum reduction of peak excitation voltage is achieved with no distortion of the excitation amplitude spectrum. The phase-scrambled frequency spectrum is inverse Fourier transformed to produce the final time domain waveform which is used to generate the electric field which excites the ions in an ion cyclotron resonance cell.